Carbon-13 nuclear magnetic resonance spectroscopic analyses of 3-aryl-3-hydroxyl-2,2,4,4-tetramethylcyclobutanones and related compounds

A series of 2-aryl-2-hydroxy-1,1,3,3-tetramethyl-5,8-dioxaspiro[3.4]octanes (1), 3-aryl-3-hydyoxyl-2,2,4,4-tetyramethylcyclobutanones (2), and 1-aryl- 2,2,4-trimethyl-1,3-pentadiones (3) were studied using C-13 NMR analyses. T he chemical shifts of C-c are dependent on the substituent groups on the ph enyl ring for compounds 1 (rho = -0.966, R-2 = 0.987) and 2 (rho = -1.378, R-2 = 0.998). The chemical shifts of C-a follow a similar trend (rho = -0.9 26, R-2 = 0.989). In the case of compounds 3, C-c yielded the opposite tren d with very poor correlation coefficiency (rho = 1.22, R-2 = 0.179). This r esult reveals the field effect of a polar bond and resonance-induced change s in pi electron-density at C-1 on the cyclobutane ring series.